The conventional video coding standards generally adopt a block based coding technique to exploit spatial and temporal redundancy. For example, the basic approach is to divide the whole source frame into a plurality of blocks, perform intra prediction/inter prediction on each block, transform residues of each block, and perform quantization and entropy encoding. Besides, a reconstructed frame is generated in a coding loop to provide reference pixel data used for coding following blocks. For certain video coding standards, in-loop filter(s) may be used for enhancing the image quality of the reconstructed frame.
A video decoder is used to perform an inverse operation of a video encoding operation performed by a video encoder. For example, an entropy encoding circuit in the video encoder is used to generate an encoded bitstream, while an entropy decoding circuit in the video decoder is used to decode the encoded bitstream. The arithmetic coding may be employed by the entropy encoding. Hence, the entropy encoding circuit refers to a probability table to perform the entropy encoding, and the entropy decoding circuit of the video decoder also refers to the same probability table to perform the entropy decoding.
Since the video content is inherently non-stationary in nature, adaptation of the probability table to account for changing statistics is critical in each of the video encoder and the video decoder compliant with an advanced video coding standard such as VP9. Further, ultra high definition (UHD) video is very popular in recent years. For example, the UHD video may have a resolution up to 8192×4320 and may have a frame rate up to 120 fps (frames per second). Hence, entropy decoding is one of the critical performance bottleneck of video processing at the video decoder. Thus, there is a need for an innovative entropy decoding design with improved entropy decoding performance.